The increased production of industrial rubber products has resulted in the accumulation of large amounts of rubber wastes which are generally disposed in dedicated landfills with the main drawbacks of environment pollution as well as of the need for large dedicated areas for storing said wastes.
It is known in the art to depolymerize waste rubber, such as tires, in an effort to reduce the volume of waste and obtain a useful byproduct. Likewise, rubber product may be devulcanized in an attempt to recycle the waste rubber.
In addition to these techniques, it is common in the art to grind the waste rubber and utilize the ground particles so obtained. These ground particles are then typically compounded with other polymeric materials in order to make final products which may be employed in a plurality of applications.
It is already known in the art to use said ground particles as an ingredient of crosslinkable elastomeric compositions. However, the crosslinked article obtained from said elastomeric compositions generally show a significant deterioration of their mechanical properties.
Many efforts have been made in the art in order to improve the mechanical properties of the above disclosed articles.
For example, International Patent Application WO 88/02313 relates to a vehicle tire having a tread portion which comprises the molded and cured product of a rubber molding composition containing from about 20% by weight to about 80% by weight, preferably from about 35% by weight to about 75% by weight, of a treated particulate rubber material comprising cured rubber particles which have been surface-treated with a liquid, sulfur-curable polymeric binder having ethylenic unsaturation and which is soluble in benzene, hexane or both, the binder softening the cured rubber particle surfaces to which it is applied. Homopolymers and copolymers of 1,4-butadiene and substituted butadienes are preferred as the liquid polymeric binder. Said treated particulate rubber material is blended with a virgin stock rubber. The above mentioned tread is said to have a wear resistance which is at least as good as and often better than the wear resistance of a tread made from virgin rubber molding stock. However, the hardness, tensile strength and elongation of the above mentioned tread were adversely affected by the addition of said treated particulate rubber material.
International Patent Application WO 2005/058615 relates to crosslinkable elastomeric compositions capable of being used advantageously in the production of crosslinked manufactured products, in particular in the production of tires, by using a vulcanized rubber in a subdivided form which has been surface treated with a silane coupling agent. In this way, it is said to be possible to obtain crosslinked manufactured products having improved mechanical properties, in particular stress at break and tensile modulus, with respect to those of crosslinked manufactured products obtained from compositions in which the vulcanized rubber is used as such (i.e. not surface-treated vulcanized rubber).
U.S. Pat. No. 5,844,043 relates to a free-flowing granular crosslinkable composition made of recycled rubber granules, rubber and oil. More in particular, said crosslinkable composition consists essentially of 100 part by weight of vulcanized rubber granules intimately mixed and coated with 3-35 parts by weight of a solution of unvulcanized polyoctenamer dissolved in oil, at a temperature below the decomposition temperature of the unvulcanized polyoctenamer, and an effective amount of a vulcanizing agent. The above mentioned crosslinkable composition is said to be easily press-molded into molded bodies having good mechanical and elastic properties. Said crosslinkable composition is said to be useful, for example, for the manufacturing of floor coverings and extrudates.
European Patent Application EP 1,031,440 relates to a pneumatic tire having a rubber sidewall composition comprising: (a) from 5 to 50 parts by weight of a recycled rubber which has an individual particle size no greater than 420 mm; (b) from 0.1 to 5 parts by weight per 100 parts by weight of recycled rubber of 3,3′-tetrathiodipronic acid; and (c) 100 parts by weight of at least one additional rubber selected from the group consisting of at least one of natural and/or synthetic cis-1,4-polyisoprene rubber, cis-1,4-polybutadiene rubber, styrene/butadiene copolymer rubber, styrene/isoprene/butadiene terpolymer rubber, ethylene/propylene/diene copolymer (EPDM) rubber, acrylonitrile/butadiene copolymer rubber and 3,4-polyisoprene rubber. The above mentioned composition is said to have good mechanical properties.
U.S. Pat. No. 6,265,454 relates to a tire component rubber formulation, said formulation comprising rubber and additives and having blended therein up to about 50 parts by weight of recycled cured ground tire rubber particles based upon 100 total parts by weight of said tire component rubber formulation and said recycled cured ground rubber particles, wherein said recycled cured ground rubber particles replace a partial amount of said tire component rubber formulation, and wherein said recycled cured ground tire rubber particles have a size of 90 U.S. Standard Mesh or smaller. The ground particles generally replace equivalent amounts of rubber and additives (such as carbon black and oil). The above mentioned tire component is said to maintain good physical properties.
U.S. Pat. No. 6,407,180 relates to a process for preparing a sulfur vulcanized rubber composition comprising: (A) homogeneously blending a pre-formed composite of carbon black and tris(2-aminoethyl) amine, with a particulate, sulfur pre-vulcanized rubber (e.g. recycled cured rubber) to form a treated vulcanized rubber composition thereof; (B) mixing about 40 parts by weight of said treated pre-vulcanized rubber composition with 100 parts by weight of at least one unvulcanized rubber to form a rubber composition blend comprising said unvulcanized rubber and said treated pre-vulcanized rubber; (C) heating said rubber composition blend for a time sufficient and at a suitable temperature to vulcanize the unvulcanized rubber composition contained therein. The invention also relates to articles of manufacture, including tires, which have at least one component comprising said rubber composition. The above mentioned rubber composition is said to have accelerated cure rates at lower than conventional temperatures.